The present invention relates generally to drift-tube linear accelerators and more particularly to variable-energy drift-tube linear accelerators.
Practical applications of proton and ion drift-tube linear accelerators are more viable now than ever before because of the development of the radio-frequency quadrupole (RFQ) accelerating structure and other technological advances. Although many of these applications would benefit from a variable energy option, drift-tube linear accelerators are not noted for this property.
The only variable-energy method known to be in routine use involves turning off later portions of the linear accelerator to provide a few discrete energies from multitank linacs. Many applications require more discrete energies than normally are available from this scheme. Further, single tank, post-coupled drift-tube linear accelerators are advocated for simplicity and reliability and any multitank arrangement to provide energy variability represents a step backward in linac technology.
Post couplers have a special property in that they can introduce a step in the electric fields. Modest perturbations to the symmetry of the post-coupler/drift-tube geometry can introduce few percent cell-to-cell changes in the fields across the post coupler. Several such perturbations on adjacent post couplers can introduce a sizable reduction in the fields over the region of a few cells. Such steps in the fields can be used to drop the beam out of synchronism with the accelerating fields and provide a variable-energy capability for the single-tank, post-coupled drift-tube linear accelerator.
It is therefore an object of the present invention to provide an improved drift-tube linear accelerator with a variable-energy capability.
It is another object of the present invention to provide a reliable post-coupler field-perturbation variable-energy drift-tube linear accelerator.